1. Field of the Invention
The present invention generally relates to liquid crystal projectors, and more particularly to an optical system of such a liquid crystal projector which has a simple construction including a polarized light separation prism and a plurality of liquid crystal panels which are each provided with a light reflection mirror mounted on a surface thereof and the liquid crystal projector is capable of providing an image of high resolution power.
2. Description of the Related Art
In conventional liquid crystal projectors, light emitted from the light source is separated into three light elements, that is, a red light element, a green light element and a blue light element, and the light is then composed into a desired color image. Thereafter, the composed color image is projected as an enlarged image onto a screen of a projection lens.
Known liquid crystal projectors are generally provided with a halogen lamp as a light source. The halogen lamp has the characteristics of emitting a light which consists of the red light element, the green light element and the blue light element in the spectral characteristics. As a result, the light having been emitted from the halogen lamp of the known liquid crystal projector is separated into the red, green and blue light elements by a plurality of optical separating members, such as red, green and blue light reflection mirrors. Thereafter, the separated light elements are transmitted through three liquid crystal panels, respectively, in order to obtain three images each reemerging in each color, and the liquid crystal panel is capable of controlling the transmissivity of each light element. The three images are next composed into a desired color image by a light separation/composition prism, and then projected on the screen as the enlarged Image by means of the projection lens.
Here, the light separation/composition prism is capable of composing the respective light elements which are received by the prism in three directions and have respective characteristic wave lengths. The light separation/composition prism is capable of separating a light into respective light elements in the case of receiving the light in a receiving direction.
Hereinafter, the known liquid crystal projector will be described in detail in conjunction with FIG. 1 which is a schematic view showing a representative example of a conventional liquid crystal projector.
As shown in FIG. 1, the liquid crystal projector includes a high luminance halogen lamp 1 as a light source for emitting the light. The light having been emitted from the halogen lamp 1 is first filtered by a 45.degree. inclined blue light reflection mirror 2 which is positioned on an optical path from the lamp 1 in a predetermined distance after the lamp 1 and adapted for separating the blue light element from the light. Here, the blue light element is reflected by the blue light reflection mirror 2 in order to reach a first 45.degree. inclined total reflection mirror 3 which is adapted to reflect the blue light element. The blue light element having been reflected by the first total reflection mirror 3 is then transmitted through a first liquid crystal panel 4. On the other hand, the light having been transmitted through the blue light reflection mirror 2 is, thereafter, filtered by a 45.degree. inclined green light reflection mirror 5, which is positioned on the optical path after the blue light reflection mirror 2, for filtering off the green light element therefrom. An accordance, the green light element is reflected by the green light reflection mirror 5 so as to be transmitted through a second liquid crystal panel 6. As a result, only the red light element is transmitted through the green light reflection mirror 5. The red light element is then reflected by second and third 45.degree. inclined total reflection mirrors 7 and 8 so as to be transmitted through a third liquid crystal panel 9.
During the transmission of the red, green and blue light elements through the three liquid crystal panels 4, 6 and 9, three images reemerge in respective colors. Thereafter, the reemerging three images are applied in each incident direction to the light separation/composition prism, such as a dichroic prism 10 in which the blue and red color images are reflected at a 90.degree. reflection angle, and the green color image is transmitted in a straight direction. Thereby, the three color images-to be composed are formed into a desired color image. The composed color image from the prism 10 is projected on a screen 12 as an enlarged image by a projection lens 11. However, a problem of the above-mentioned conventional liquid crystal projector is that it includes a halogen lamp of a high luminance which emits light having a spectral characteristics in which the red light element of the light has a more intense radiation than those of the other light elements. Therefore, in an effort to solve the problems resulting from the light source, the optical system of the conventional liquid crystal projector is such arranged so that the length of the optical path of the red light element is longer than those of the other light elements as shown in FIG. 1 in order to compensate for the intense radiation of the red light element. However, the compensation for the intense radiation of the light elements has not been sufficient. Thus, the conventional liquid crystal projector has a disadvantage in that the projected image on the screen almost appear to be red. Thereby, a high resolution image is prevented from being obtained. In addition, it is difficult to manufacture the light separation/composition prism such as the dichroic prism used in the conventional liquid crystal projector. Furthermore, the dichroic prism is a costly, heavy and fragile element. The conventional liquid crystal projector additionally has a relatively complex construction from using a plurality of liquid crystal panels.